Means for suppressing flash-overs in rotary-converter systems



N. w. STORER. MEANS FOR SUPPRESSING FLASH-OVERS- IN ROTARY CONVERTER SYSTEMS.. I

. APPLICATION FILEDJULY 25,1918- 1 1,392,087. PatentedSept. 27, 1921..

2 SHEETS-SHEET 1.

INVENTOR E I WITNESS s v A BY 0368M N. w. STORER.

MEANS FOR SUPPRESSING FLASH-OYERS IN ROTARY CONVERTER SYSTEMS. APPLICATION FILED JULY 25, 1918.

1,392,087. PatentedSept. 27,1921.

2 SHEETSSHEET 2.

V YfV I W iii 35 WITNESSES: INVENTOR M ATTIORNEY UNITED STATES PATENT OFFICE.

NORMAN W. s'ronnn, or PITTSBURGH, PENNSYLVANIA, As'sIeNoR TO WESTING- HOUSE ELECTRIC & MANUFACTURING VANIA.

co urANY, A CORPORATION or PENNSYL- Application filed July 25,

To all whom it may concern .1

Be it known that I, NORMAN W; S'ronnn, a citizen of the United States, and a resident of Pittsburgh, in the county of Allegheny, and State of Pennsylvania, have invented a new and useful Improvement in Means for Suppressing F lash-Overs in Rotary-Con verter Systems, of which the following is a specification.

invention relates to means for minimizing or preventing commutator flashovers in rotary-converter systems, and it has for its object to provide a system of the character designated wherewith the desired result may be secured in a simple, effective and inexpensive manner. I

Figure l of the accompanying drawing is a diagrammatic View of two rotary converters, together with associated load and supply circuits and auxiliary apparatus embodying two forms of my invention; and Figs. 2,3 and 4 are similar views of other forms of my invention.

In my copending application, Serial No.

203,527, filed Nov. 28, 1917, I describe and claim means whereby a plurality of points in the armature winding of a direct-current generator are interconnected in the event of abnormal current flow therefrom, whereby the magnetically stored energy of the armature winding is immediately dissipated and the field magnetism is neutralized. By thismeans, the "energy, which would otherwise .be available for initiating and maintaining flash-overs, is so promptly and effectively dissipated as to largely minimize or entirely obviate this disastrous action.

In my copending application, Serial No. 222,083 filed March 13, 1918,I describe and claim theapplication of similar means to a rotary converter for a similar purpose. In order to obviateshort-circuiting of the transformer secondary winding, I disclose the application of suitable. auxiliary slip rings to the rotary-converter armature these sliprings preferably beingtapped substantially midway between the main alternating-cub rent-supply slip-rings. By placing the fiashover suppressing short-circuit'upon the auxiliary slip-rings, the machine energy is quickly dissipated without short-circuiting the transformer secondaries.

Infurther investigating this general sub- Speoification of Letters Patent.

Patented Sept. 27, 1921.

1918. Serial No. 246,758.

jectmatter, I have found that a portion of the flash-over diflicult-y arises from the energy magnetically stored within the supply transformer, as well as from that stored in the converter itself'and, furthermore, upon the occurrence of a flash-over, energy is supplied thereto from the system. It becomes desirable, therefore, that effective means he provided for the reduction or prevention of energy flow from all three of these sources to theflash-over are.

I find that, if a portion or all of the leads between a supply transformer and. a rotary converter be promptly interconnected upon the occurrence of flash-over conditions within the converter or if, under like conditions, an impedance device be inserted in said leads, flash-overs may be effectively suppressed without impressing undue current stress or strain upon the primary side of the supply transformers, particularly if, as

is usually the case, the transformers embody from 15 to 20% reactance. As an extreme case of the insertion of impedance in the supply leads, they may be opened, this being equivalent to the insertion of infinite resistance.

After'a short interval of time, the flashover preventing means may be returned to the normal position, thus again putting the converter into service or, if preferred, the adjustment maybe such that the alternating-current circuitrbreaker opens, thus freeing the ntire system.

Not only is the present system susceptible of application to a single rotary-converter, as above described, but, furthermore, I may supply the same to a plurality of rotary converters, deriving their alternating current from distinct secondary windings of a supply transformer, as is occasionally the case. Under these conditions, the close inductive relation existing between the difierent secondary transformer windings effectively transfers a large portion of the stored energy of the transformer to the energy circuit first to come into action.

Referring to Fig. 1 of the accompanying drawings for amore detailed, understand ingof my invention, a rotary converter is shown at2 embodying an armature 8 and an exciting field-magnet system 4 and, similarly, arotary converter is shown at 5 embodyin an armature 6 and a field-exciting system l.

Energy for the operation of the converters 3 and 6 is derived through a transformer 8 embodying primary windings 9 and two dis tinct sets of secondary windings 10 and 11.

The secondary winding 10 is connected to energize the armature winding of the converter 2 through suitable slip-rings, as is the usual practice, although, for simplicity and clearness, I have indicated the supply leads 12, 13 and 14 as permanently attached to points in the windings. In like manner, supply leads 15, 16 and 17 connect the secondary winding 11 to the winding of the armature 6.

Direct current is derived from the winding of the armature 3 through a commutator of any desired construction and supplied to direct-current buses 18 and 19, although, in order to still further enhance the simplicity and clearness of the draw ing, I have shown the direct-current brushes 2020 as bearing directly upon the armature winding, in accordance with familiar drafting practice. 'In like manner, directcurrent brushes 21-21 derive current from the winding 6 for supply to the same directcurrent buses 18 and 19.

A direct-current circuit-breaker 22 is shown connected between the winding of the armature 3 and the bus 19 and, in like manner, a direct-current circuit-breaker 23 is inserted between the winding of the armature 6 and the same bus. An alternatingcurrent circuit-breaker 24 may be inserted in the supply leads of the transformer primary winding 9, if desired.

A relay switching device 25 is arranged to have its operating winding energized by the load current of the converter 2 and, when energized to or above a predetermined degree, serves to interconnect the supply leads 12, and 14, as through conductors 26, 27 and 28. In like manner, a relay switching device 29 serves to interconnect the supply leads 15, 16 and 1", as through conductors 30, 31 and 32, upon the occurrence of flash-over producing means within the comnrter. The operating winding of the relay 29 is in circuit with the field winding of the exciting pole 7 of the converter 5, thus rendering the relay 29 sensitive to flash-overproducing conditions in the manner fully discussed in a copending application of C. M. Moss, Serial No. 242,623, filed June 20, 1918, and assigned to the Vestinghouse Electric & Manufacturing Company. A marked advantage of this method of operating the relay over the method shown in connection with the converter 2 is that the device is operative upon internal short circuits in the machine 6, the effect of a short-circuit being to change the armature field, radically decreasing the citing field and, therefore, causing a pronounced increase in the field current in accordance with Lenzs law.

The switching devices 25 and 29 are preferably quick-acting in their response to a current increase, preferably being so designed as to establish a good conducting path between the associated supply leads well within the time required for a portion of the armature winding to pass from one brush to the other or, in other words, to pass from a condition of maximum positive potential to a condition of negative po tential.

Having thus described the arrangement of a system embodying my invention, the operation is as follows: It being assumed that the current taken from the buses 18 and 19 exceeds a predetermined amount so that, for example, the switching device 25 closes. The supply leads 12, 13 and 14, interlinking the converter 2 with the supply transformer secondary windings 10, are promptly interconnected and there is an instantaneous and pronounced flow of circulating currents from the secondary windings 10 to the point of interconnection and from the winding of the armature 3 to the same point. The flow of current from the supply system is promptly shunted or bypassed around the converter 3 so that it is ineffective in supporting the flash-over arc. Furthermore, the working flux of the transformer 8 is promptly and radically reduced in value, thus radically reducing the mag netically stored energy of the transformer itself contemporaneously with the decrease of magnetically storBd energy within the converter. substantially all of this magnetically stored energy being dissipated in the heating effect of circulating currents flowing through the temporary short circuit thus established.

During the same period of time, the magnetic interconnections within the transformer 8 are such that the energy interlinked with the secondary winding 11 is also dissipated, thus reducing the tendency to flash-over in the machine 5 as well as in the machine 2.

In due time, the circuit breaker 22 associated with the machine 2 opens the direct current circuit, thus completely removing the machine 2 and causing the switching device 25 to open and, if desired, said breaker may be arranged to directly open the interconnection, as through suitable auxiliary contact members. The breaker 22 may, furthermore, simultaneously open the field circuit of the machine 2, all as described in detail in the aforementioned applications.

The operation of the protective apparatus associated with the converter 5 will be obvious from the foregoing description. A sudden increment of load current within the armature winding-of the. armature fi,

from any causewhatsoever, either an internal short-circuitlor an external: short-'cir cuit, demagnetizes the field pole 7 and causes an inductive rise'of current in'the field circuit. The switch 29 at once closes, interconnecting the supply leads and protecting themachine '5, at the same time protecting the machine 2 by reason of the inductive relationship between the secondary -.windin s l0 and 11.

if desired, the adjustment may be such that the alternating-current circuit-breaker 24 opensprior to the direct-current circuitbreakers, thus'relieving the entire bank of rotary converters, uponthe operation of the fiash-over-suppressing circuit.

Upon casual consideration, it would seem that disastrous effects would follow the clirect interconnection of the second'ary windings of a supply transformer but if, as is frequently the case, the inherent reactance of the transformers amounts to or 30%,

as, isemployed, for example, in the control of, the output .voltage of the converter by the alternating-current reactance method, the total current flowing: on the primary side? of the transformer is maintained with- 33'from 'a transformer '8, and a direct-curren't loadf'circuit is connected to thebrushes in the usual -nianner. Impedance devices 37,38 and 39yare'inse-rted in the supply leads from the transformer 8 to the converter and these impedance devices are normally short-circuited by the contact'members of a relaydevice 40. Thexoperating winding of th'e device 40' is in-circuit with the field winding 36, whereby the impedance devices 37,138 and 39*are first insertedin circuit,

upon the flow 'of such abnormal :current in the field circuit aswill actuate the device 40. and the armature winding of the rotary converter is "then short-circuited through the back contacts of the device 40 for the dissipation of the stored energy. I

Thei-mpedance devices 37, 38 and 3 9 are indicated as ohmic resistors but they may be either condensive or inductive in nature if desired. These impedance devices may well be those normally employed in reducing the voltage supplied to the converter during starting and, to this end, means may be;

provided such as an operating handle 41,

whereby the impedance devices may be rendered effectiveat the will of the operator.

In the form of my invention shown in Fig.

3, the general arrangement of circuits is as before except that a relay device 42, when opened, servesto first disconnect the trans; former from the converter, and to then short-circuit the armature winding of the rotary converter, the device 42 being, in effect, an alternating-current circuit-breaker of the selfclosing type provided with back contact members. This breaker may be rendered quick opening and slow closing, as by a biased dash-pot 43 and if the time re 7 quired for closing is quite appreciable such, for example, as a second or more, the con verter 33 will, in most cases, clear itself of flash-over conditions and be prepared for. the resumption of service upon the closing of'the circuit breaker 42. p T i In the system of Fig. 4-, a relay device ,io isarranged to short-circuitan auxiliary secondary winding 46 on the transformer 8 upon the occurrence of overload conditions, thus largely eliminating the flow ofload current through the transformer and induc-- tively absorbing the stored energy-fromthe working secondary winding 9., The operating winding of t e relaydevice 45 may be. energized by any of the above-described methods or, ass'hown, it maybe energized from the terminals ofan auxiliary winding 47 mounted on the field pole-35.- This latter connection is of advantage where the normal changes in the field excitation of the winding 36 are quite pronounced, although gradual. Such changesin the energization of the field winding 36 produc'e little or no effect upon thev winding 47,"although the abrupt change in' the exciting field flux caused by fiash-over conditions induces a pronounced electromotive'force in the winding 47, irrespective of thecurrent then flow in in the winding 36. yi v i I j rom aconsideration of the above-de scribed circuits and of the circuits shown in the copending applications to which reference ismade, it will be apparent that there 1s :a large number of different combinations and arrangements that may be effected for,

bringing about the general results hereinproduced, and these possibilities may be analyzed as follows. In the first place, there 7 are three points, from whichjthe operating. effect maybe produced, namely, from the-al-' ternating-current mains, from the direct-current mains and from theexciting-field circuit. The operating-eifectmay. be'derived either directly or inductively, as by the use of. current transformersassociated with the alternating-currenttsupply mains or by an auxiliary winding placed upon the supply transformer or upon the exciting fi-eldpole.

Having derived the desired operating effect, it may be applied in short-circuiting the armature winding itself, either at the I tap points, as by short-circuiting the slip rings, or by interconnecting points other than the tap points. The operating effect may further be employed to insert either finite or infinite impedance in the supply leads between the transformer and the corn verter and it may be employed to shortcircuit an auxiliary winding placed directly upon the armature, as dlsclosed in a copending application of B. G. Lamme, Serial No. 2%,422, filed June 17, 1918, and assigned to the Westinghouse electric 6t lVlanufacturing Company or by short-circuiting an auxilia-ry winding upon the supply transformer.

In construing the breadth of the present invention, it is desired that all of the above possible combinations be borne in mind, whether completely described and illustrated or not, and that the claims be construed accordingly, it obviously being needless to encumber the present description with a detailed description of all the possible combinations.

If desired, as in an automatic substation,

means may be provided for again automati-f cally placing the system in operation but such means constitute no part of the present invention and I deem it unnecessary, therefore, to encumber the disclosureand discus sion with a detailed description thereof.

I claim as my invention:

l. The combination with a rotary converter, of a source of alternating current and a load circuit connected thereto,-respectively, and means for simultaneously impos-' ing a relatively high-impedance short-circuit upon said source and a relatively lowimpedance short-circuit upon said converter upon the occurrence of flash-over producing conditions within said converter.

2. The combination with a rotary con verter, of a supply transformer therefor, a

load circuit connected thereto, and means for interconnecting at least two supply leads between said transformer and said converter upon the occurrence of abnormal current flow in said load-circuit.

The combination with a rotary conconnection in less time than is required for a given point in th armature winding of said rotary converter to pass from a condition of maximum positive potential to a condition of maximum negative potential.

5. The combinationwith a rotary converter, of a supply transformer therefor, a load-circuit connected thereto, a relay device arranged to interconnect at least two supply leads between said transformer and said converter upon the occurrence of abnormal current flow in said load circuit, said device being designed to complete said interconnection in less time than is required for a given point in the armature winding of said rotary converter to pass from a condition of maximum positive potential to a condition of maximum negative potential, and a relatively slow-acting circuit-breaker arranged to open said load circuit upon the occurrence of said abnormal current flow.

6. The combination with a dynamo-electric machine of the commutator type, of means responsive to flash-producing conditions for automatically interconnecting a plurality of points in the armature winding in such manner as to form a symmetrical close-circuited polyphase winding.

7. The combination with a dynamo-electric machine of the commutator type, of means responsive to flash-producing conditions for automatically producing a polyaxially close-circuited winding for screening the field flux from the armature conductors undergoing. commutation.

8. The combination with a supply transformer,'of a plurality of rotary converters connected to derive energy therethrough, and a device dynamically associatediwith said transformer and adapted to dissipate the stored energy thereof and of said machines upon the flow of abnormal current in one of said machines.

9. The combination with a supply transformer, ofa plurality of rotary converters connected to derive energy therethrough, and a device dynamically associated with said transformer and adapted to dissipate the stored energy thereof and of said machines upon the flow of abnormal current in any one of said machines.

10. The combination with a rotary converter, of asupply transformer connected to transmit energy thereto, a load circuit connected to be energized from said rotary converter. and means for simultaneously dissipating the stored energy of both pieces of apparatus upon the flow of abnormal current in'said load circuit.

In testimony whereof I have hereunto subscribed my name this 22nd day of July,

NORMAN W. STORER. 

